PROJECT SUMMARY/ABSTRACT Alcohol use is associated with significant personal and socioeconomic costs (accounting for more than 5% of global disease burden as well as worldwide deaths). Alcohol use initiation, progression to heavy episodic drinking, and early onset alcohol use disorder commonly emerge during adolescence and young adulthood. This developmental period of risk is theorized to result from typical patterns of regionally asynchronous brain maturation (i.e., rapid and early development of limbic regions alongside relatively immature prefrontal and multimodal association cortices) resulting in a diminished ability to suppress inappropriate emotions, desires, and actions when salient environmental cues are present. During later young adulthood the stabilization, reduction, or desistance of heavy use typically occurs alongside maturing cognitive control and emotional regulation abilities coinciding with cortical development. Brain maturation may also be influenced by alcohol use. However, whether alcohol use alters brain maturation and/or results from individual differences in neural development attributable to predipsositional genomic background is unclear and can only be addressed by genomically-informed longitudinal research with extensive alcohol phenotyping. In this 2-year R21, we propose to add genome-wide association study (GWAS) content to 2 longitudinal neuroimaging studies of adolescents and young adults (n=696; spanning ages 12-33 with annual neuroimaging and biannual alcohol characterization) to examine whether brain changes during adolescence and young adulthood associated with alcohol use may represent polygenic risk factors and/or represent consequences of heavy alcohol exposure. Disentangling the contributions of predisposing factors from consequences of alcohol on structural brain trajectories will inform our etiologic understanding of alcohol use during adolescence and young adulthood that could contribute to alcohol- related policy, education, nosology, prevention, and treatment. Primary deliverables from this project will be manuscripts examining whether polygenic propensity to alcohol use, as well as risk for impulsivity and negative affect and deficits in cognition, modify trajectories of brain maturation and further alter the course of youth alcohol engagement. Further, due to the extensive scope of longitudinal data available in these studies (e.g., other neural phenotypes, psychiatric, sleep, trauma, biosensor assessments), the addition of GWAS data will provide benefits to the broader research community through data sharing (e.g., dbGaP) and contribute to consortia-based gene discovery efforts (e.g., ENIGMA, PGC).